The present invention relates to an image display device.
An image display device is known that has an ABL circuit and a contrast adjusting circuit. Especially, the ABL circuit is known that performs control process so that an average display brightness of a screen does not become too large for convergence of beams, or so as to refrain a consumption electric power and the like.
For example, Japanese Patent Laid-open application No. 2000-221941 discloses a configuration that performs the ABL, in which an automatic brightness control circuit is used, and also a brightness level is adjusted for pixel data by each of pixels of an image to be sequentially supplied from an A/D converter so that an average brightness of the image displayed on a screen of PDP lies within a predetermined range. Here the brightness level is adjusted before each of ratio between emission numbers of each of sub-fields is set in a non-linear manner and an inverse-γ conversion is performed.
Generally, an image signal is transmitted or recorded after following γ conversion under an assumption that the image signals are displayed using a CRT display device as illustrated in FIG. 12. The γ conversion allows the image signals to be non-linearly converted such as converted by power of 0.45 corresponding to input-emission characteristics of the CRT display device. When such image signals are displayed on a display device such as SED, FED or PDP having linear input-emission characteristics, an inverse-γ conversion serving as conversion represented by power of 2.2 as illustrated in FIG. 13 is needed for inputted signals. On the other hand, when inputted signals are displayed on a display device such as LCD, an appropriate conversion is performed that meets the characteristics of such a display device.
FIG. 14 shows a block diagram of an image signal processing device to be provided in a normal image display device having luminescence characteristics being different from luminescence characteristics of CRT for inputted signals such as SED, FED, PDP or LCD. An actual image signal processing device has many other processing circuits. However, in FIG. 14, only circuit blocks are picked up relating to the present invention.
An image signal processing device illustrated in FIG. 14 is provided with an A/D converter 1001, a signal processing section 1002, an average brightness detecting section 1003 and a gain calculating section 1004. The A/D converter 1001 inputs analog inputted image signals s101 and outputs digital image signals s102. The signal processing section 1002 inputs the digital image signal s102 and performs signal processing such as inverse-γ conversion, brightness/chromaticity-adjustment or a contour emphasis processing and thereafter outputs display signals s103. The average brightness detecting section 1003 inputs the digital image signals s102, detects an average brightness of each of frames, and thereafter outputs an average brightness control signals s104. The gain calculating section 1004 inputs an average brightness signal s104 and outputs a brightness control signal s105.
The A/D converter 1001, the signal processing section 1002, the average brightness detecting section 1003 and the gain calculating section 1004 are operated based on various timing signals generating according to a synchronous signal of the input image signals s101.
However in the configuration of FIG. 14, the average brightness can be obtained by summing up the digital image signals s102 while an actual image displayed using a display device is formed using display signals s103 that are signal-processed by various process manners, in which the inverse-γ conversion is typical. Especially, through the inverse-γ conversion, non-linear conversion like conversion of power of 2.2 as illustrated in FIG. 13 is performed. As a result, the average brightness is more lowered and also there is no one-to-one relationship between the average brightness of the digital image signal s102 and the average brightness of the display signal s103 processed by the inverse-γ conversion. Therefore the average brightness signal s104 to be detected by the average brightness detecting section 1003 has an error with relative to the average brightness to be actually displayed on the display device, resulting in that accurate average brightness information has not been able to be obtained.